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EFFECT OF THYROID DYSFUNCTION ON METABOLIC RESPONSE IN
TYPE 2 DIABETIC PATIENTS
Dr. Asmabi Makandar1*, Dr. Amit D. Sonagra2
1. Assistant professor, Department of Biochemistry, Al Ameen Medical College, Vijapura,
karnataka, India.
2. Assistant professor, Department of Biochemistry, GMERS Medical College, Dharpur-Patan,
Gujarat, India.
BACKGROUND: Diabetes and thyroid disorders are common disorders of endocrine system in
the world. Occurrence of both disorders is also common. Alteration in thyroid hormone levels
can affect body metabolism, glycemic control and insulin sensitivity in diabetic patients. So the
study is required to find association between various parameters among patients with thyroid
disorders and diabetes.
OBJECTIVE: To find out the prevalence of thyroid dysfunction in type 2 diabetic patients and
to evaluate association between thyroid dysfunction, Fasting serum glucose, glycosylated
hemoglobin and lipid profile in type 2 diabetic patients.
MATERIALS AND METHODS: A 100 type 2 diabetic patients were selected for this study.
The parameters measured were fasting serum glucose (FSG), glycosylated hemoglobin (HbA1c),
total cholesterol (TC), triacylglycerol (TAG), low-density lipoprotein cholesterol (LDL-C) and
high-density lipoprotein cholesterol (HDL-C).
RESULTS: Among the 100 type 2 diabetic patients studied, 32% of the patients have abnormal
thyroid hormone levels and 68% have normal thyroid hormone levels. Among the 32% of
diabetic patients with abnormal thyroid hormone levels, 22% of them have hypothyroidism (8%
clinical hypothyroidism, 14% subclinical hypothyroidism) and 10% of patients have
hyperthyroidism (4% clinical hyperthyroidism, 6% subclinical hyperthyroidism). The levels of
FSG, HbA1c, TC, TAG, LDL-C are increased significantly (p< 0.05) in diabetic patients with
thyroid dysfunction when compared with euthyroid diabetics, whereas HDL-C levels are
decreased significantly (p<0.05) in diabetic patients with thyroid dysfunction than euthyroid
diabetics.
CONCLUSION: Our findings suggest that screening of thyroid dysfunction in type 2 diabetic
patients is necessary because thyroid dysfunction when associated with diabetics can produce
significant metabolic disturbances.
KEYWORDS: Type 2 diabetes mellitus, Thyroid dysfunction, Dyslipidemia, Glycosylated
hemoglobin.
Corresponding author: Dr. Asmabi Makandar, Assistant professor, Dept of Biochemistry, Al
Ameen Medical College, Athani Road, Vijapura - 586108, Karnataka, India.
[email protected]
INTRODUCTION:
Diabetes mellitus is an important health problem affecting major populations worldwide.
It is characterized by absolute or relative deficiencies in insulin secretion and/or insulin action
associated with chronic hyperglycemia and disturbances of carbohydrate, lipid, and protein
metabolism1.
The WHO estimate of diabetes prevalence for all age groups worldwide was 2.8% in
2000 and 4.4% in 2030. The total number of people with diabetes is projected to rise from 171
million in 2000 to 366 million in 20302. Factors such as sedentary lifestyle, dietary
modifications, ethnicity, hypertension and obesity have led to a dramatic increase in the
incidence of diabetes mellitus, especially in the 21st century3. India leads the world with largest
number of diabetic subjects earning the dubious distinction of being termed the “diabetes capital
of the world”4.
Thyroid disorders are also very common in the general population and it is second only to
diabetes as the most common condition to affect the endocrine system. As a result it is common
for an individual to be affected by both thyroid diseases and diabetes5. A number of studies have
estimated the prevalence of thyroid dysfunction among diabetic patients to be varying from 2.2
to 17 %6,7. However, recent studies have estimated much higher prevalence of thyroid
dysfunction in diabetes i.e. 24%, 30%, 43%, 45%, and 46.5% respectively [8,5,9,1,10].
Lipid disorders are common in diabetes mellitus, and play crucial roles in the
development of diabetic cardiovascular complications. Diabetic dyslipidemia is characterized by
hypertriglyceridemia, increased levels of very low density lipoproteins (VLDL), LDL-C and
decreased levels of HDL-C11.
Presence of thyroid dysfunction may affect diabetes control. Hyperthyroidism is typically
associated with worsening of glycemic control and increase insulin requirements. In
hypothyroidism, the synthesis and release of insulin is decreased. The rate of hepatic glucose
output is decreased probably due to reduced gluconeogenesis12,13.
Thyroid disorders are known to influence lipid metabolism. Overt or subclinical
hypothyroidism is associated with hypercholesterolemia mainly due to elevation of LDL-C level,
whereas HDL-C is usually normal or even elevated14,15. Abnormalities of lipid metabolism in
hypothyroidism contribute to the development of CVD. Subclinical hyperthyroidism may
increase the risk of cardiac arrhythmias and exacerbate angina. On the other hand,
hyperthyroidism is accompanied by decrease in serum levels of total cholesterol, LDL-C and
HDL-C12. HbA1c is normally used for assessment of diabetic control, and the American
Diabetes Association recently recommended its use for diagnosing diabetes and pre-diabetes.16
Since thyroid hormone regulate metabolism and diabetes can alter metabolism of food stuff, the
metabolism of organisms may be further affected of the combination of thyroid disease and
diabetes. We aimed to evaluate association between thyroid dysfunction, lipid profile and
glycosylated hemoglobin in type 2 diabetic patients.
MATERIALS AND METHODS:
A cross sectional study was carried out on 100 type 2 diabetic patients. All the patients
were confirmed diabetics who previously had fasting blood glucose levels >120 mg/dl on more
than two occasions based on the American diabetes association(ADA) 2010 criteria for diagnosis
of DM[17] and who were receiving treatment such as insulin, oral hypoglycemic drugs or physical
exercise therapy for diabetes mellitus. General health characteristics such as age, sex, smoking
status, menopausal status, alcohol consumption, and dietary habits (particularly as related to
preference) were investigated by a self-administered questionnaire. The study excluded the
Patients having history of type 1 diabetes mellitus, those with known history of thyroid
dysfunction and Patients with liver disease, renal disease, hypertension and pregnancy. All
subjects were informed about the objectives of the study and what roles they were expected to
play. This study was approved by institutional ethical committee.
Biochemical investigations:
Collection of blood sample: Under all aseptic precautions, using a sterile disposable syringe
about 5 ml of venous blood was drawn from subjects after overnight fasting. 3 ml of blood was
taken into plain vacutainer and was subjected for centrifugation, serum was separated which was
used for estimation of FSG, thyroid profile and lipid profile. 2 ml blood was taken into EDTA
containing vacutainer and was used for estimation of HbA1c.
Methods of estimation: FSG was measured by Glucose oxidase (GOD-POD) method [18]. Serum
T3, T4 and TSH were estimated by Chemiluminescence Immunoassay Method (CLIA) in CLIA
analyzer19. Serum TC, TAG and HDL-C were measured by enzymatic method using phenol-
aminoantipyrine. The serum LDL cholesterol was determined using Friedwald’s formula20.
HbA1c is by Cation-Exchange resin method and the kit was purchased from Euro diagnostics
Bangalore21. FSG and Lipid profile were estimated in Autoanalyzer ERBA MANNHEIM EM
200 and HbA1c in Semiautoanalyzer ERBA Chemtouch.
Classification of the values into high, low, or normal thyroid hormone level was based on
the following criteria. Subjects classified as having high levels of thyroid hormones had T3
values >2ng/ml, T4 value > 12µg/dl or TSH< 0.2 µIU/ml or both. Those classified as having
hypothyroidism had T3 values < 0.5 ng/ml, T4 values < 4.8 µg/dl or TSH values >5.4 µIU/ml or
both. Subject grouped as euthyroid had T3, T4 and TSH values within the range of 0.5 – 2.0
ng/ml, 4.8 – 11.6 µg/dl and 0.28 – 5.45 µIU/ml respectively.
For serum lipid reference level, National Cholesterol Education Programme (NCEP)
Adult Treatment Panel III (ATP III) guideline was referred. According to NCEP-ATPIII
guideline, hypercholesterolemia is defined as TC>200 mg/dl, high LDL-C when value >100
mg/dl, hypertriglyceridemia as TAG >150 mg/dl and low HDL-C when value <40 mg/dl.
Dyslipidemia was defined by presence of one or more than one abnormal serum lipid
concentration22.
STATISTICAL ANALYSIS: Results are expressed as Mean ± SD, and range values for
continuous data, number and percentage for discrete data. Prevalence of thyroid dysfunction was
expressed as percentage with 95% confidence interval (CI). One way ANOVA was used for
multiple group comparison, followed by Post hoc-Turkey’s test for group wise comparison.
Unpaired t-test was used for two group comparison. For all the tests P value of < 0.05 was
considered for statistical significance. SPSS version 16 was used for data analysis.
RESULTS:
Among the 100 type 2 diabetic patients studied, 47 were males and 53 were females with
mean age of 55.5 ± 6.2 years. Graph 1 shows that among the 100 type 2 diabetic patients studied,
32% of the patients have abnormal thyroid hormone levels and 68% have normal thyroid
hormone levels. Among the 32% of diabetic patients with abnormal thyroid hormone levels, 22%
of them have hypothyroidism (8% clinical hypothyroidism, 14% subclinical hypothyroidism)
and 10% of patients have hyperthyroidism (4% clinical hyperthyroidism, 6% subclinical
hyperthyroidism). This is in accordance with studies [1,5,8,9,10].
Graph 1: Prevalence of thyroid dysfunction in type 2 diabetic patients
80%
70%
60%
50%
40%
30%
20%
10%
0%
68%
22%
10%
Euthyroid Diabetics
Hypothyroid
Diabetics
Hyperthyroid
diabetics
% of Diabetic patients
After the thyroid function test the patients are categorized into two groups based on
thyroid hormone levels.
Group I: Diabetic patients with normal thyroid hormone levels (Euthyroid diabetics).
Group II: Diabetic patients having abnormal thyroid function (including both Hyperthyroidism
and Hypothyroidism).
Table 1. Shows levels of FSG, HbA1c and lipid profile in diabetic patients with euthyroidism
and diabetic patients with thyroid dysfunction
Parameters
Group I (Diabetics with
Euthyroidism n=68)
Group II (Diabetics
with thyroid
dysfunction n=32)
Mean
difference
t value
p value
FSG
149.5±12.3
195.8±21.6
46.3
12.49
< 0.001
(mg/dl)
HbA1c
124-177
8.1±0.6
160-250
11.2±1.1
3.1
16.5
< 0.001
(%)
TC
6.9-10.2
217±22.5
9.6-13.6
273.6±38.7
56.7
8.5
< 0.001
(mg/dl)
TAG
165.7-265.6
185.4±38.7
185.6-375.1
230.5±57.4
45.1
4.42
< 0.001
(mg/dl)
LDL-C
112.1-189.6
143.1±30.6
96.3-406.4
195.8±37.6
52.7
7.47
< 0.001
(mg/dl)
84.4-262.6
126.9-280.9
HDL-C
38.2±7.2
32.5±6.1
(mg/dl)
27.1-59.8
20.2- 43.5
5.7
4.27
< 0.001
Table 1. Shows that the levels FSG, HbA1c, TC, TAG and LDL-C were increased in
diabetic patients with thyroid dysfunction when compared to diabetic patients with euthyroidism
and is of statistical significant (p< 0.001),whereas serum HDL-C level is decreased and is of
statistical significant (p<0.001).
Table 2. Shows levels of FSG, HbA1c and lipid profile in type 2 diabetic patients with
hypothyroidism and hyperthyroidism
Diabetics with Hyper
thyroidism
200.9±18.1
(n=15)
170-241
11.2±1.1
Mean
difference
7.9
t value
p value
1.22
0.23 NS
(mg/dl)
HbA1c
Diabetics with
Hypothyroidism
193±23.2
(n=27)
160-250
11.1±1.1
0.1
0.28
0.78 NS
(%)
TC
9.6-13.6
280.3±38.2
9.8-13
261.5±38.0
18.8
1.53
0.14 NS
(mg/dl)
TAG
216.4-375.1
230.8±48.9
185.6±327.2
229.9±72.3
0.9
0.04
0.97 NS
(mg/dl)
LDL-C
154.4-314.9
204.7±36.9
96.3-406.4
179.6±34.3
25.1
2.21
0.05 NS
(mg/dl)
HDL-C
137.5-280.9
32.4±6.1
126.9-244.8
32.7±6.3
0.3
0.17
0.86 NS
Parameters
FSG
(mg/dl) NS- Non significant
20.2-43.5
S- Significant
21.3- 40.8
The levels of FSG, HbA1c, TG, TAG, LDL-C and HDL-C did not differ significantly
between diabetic patients with hypothyroidism and hyperthyroidism (p> 0.05).
DISCUSSION:
The present study has shown a very high prevalence of thyroid dysfunction among type 2
diabetic patients, hypothyroidism being more common than hyperthyroidism. Our results are in
accordance with Pasupathi P et al1, Singh G et al5, Mazin Z et al8, Swamy RM et al9, C.E.J
Udiong et al 10 and abdul wahab sheikh et al23.
Several studies have been conducted to find out the mechanism of thyroid dysfunction in
diabetic patients. DM appears to influence thyroid function in two sites; firstly at the level of
hypothalamic control of TSH release and secondly at the conversion of T4 to T3 in the peripheral
tissue. The presence of both raised and low levels of thyroid hormones levels in diabetics may
also be due to modified TRH synthesis and release and may depend on the glycemic status of the
diabetics studied. Glycemic status is influenced by insulin, which is known to modulate TRH and
TSH levels. Stress, which is associated with diabetes, may also cause changes in the
hypothalamus-anterior pituitary axis in diabetics. Marked hyperglycemia and hyperinsulinemia
are known to suppress hepatic enzyme T4-5 deiodinase, leading to decrease conversion of T4 to
T3. Insulin has been associated with anabolic activity, enhance TSH turn over a protein hormone.
Some of the oral hypoglycemic agents commonly used by the diabetic patients such as
Phenylthioureas are known to suppress the level of FT4 and T4, while causing raised levels of
TSH8,10.
Table 1. Shows that the levels of fasting serum glucose and HbA1c in type 2 diabetic
patients with thyroid dysfunction were increased as compared to diabetic patients with
euthyroidism and is of statistical significant (p < 0.001). Thyrotoxicosis is diabeticogenic factor
and long term thyrotoxicosis has been shown to cause B-cell dysfunction. In hyperthyroidism
there is elevation in the rate of glucose absorption, production (and utilization) and glycogen
degradation leading to decreased glycogen level, but insulin resistance, degradation and
requirements are increased and there is increased secretion with exaggerated effects of glucagon
and adrenaline on the liver, all these changes may lead to diabetic ketoacidosis in state of
insufficient insulin supply. In patients with undetected DM, hyperthyroidism can unmask
diabetes because glucose levels may be elevated. For these reasons the dosage of oral
antidiabetic drugs (OAD) and insulin should be increased in diabetic patients with thyroid
disease.
In hypothyroidism there is reduction in the rate of glucose absorption, gluconeogenesis
and glucose production (and utilization) and glycogen degradation leading to increased glycogen
level. Additionally, insulin half-life will be prolonged with increase in its level and reduction in
insulin requirement. Glucose level will be stabilized during treatment of hypothyroidism but the
risk of recurrent hypoglycemia will increase if insulin dose is not decreased8.
The mean levels of TC, TAG and LDL-C were increased in diabetic patients with thyroid
dysfunction as compared to diabetic patients with euthyroidism and is of statistical significant
(p< 0.001), whereas HDL-C level is decreased and is of statistical significant ( p < 0.001). These
results are in consistent with previous studies13,24. But our study showed no significant difference
between the levels of FSG, HbA1c and lipid profile in diabetic patients with Hypothyroidism and
hyperthyroidism. Further studies are required to find out effect of thyroid dysfunction in type 2
diabetic patients.
Several factors are likely to be responsible for diabetic dyslipidemia: insulin effects on
liver apoprotein production, regulation of lipoprotein lipase (LpL), actions of cholesteryl ester
transfer protein (CETP), and peripheral actions of insulin on adipose and muscle25.
Thyroid hormones influence all aspects of lipid metabolism including synthesis,
mobilization, and degradation. Thyroid hormones regulate the activity of some key enzymes of
lipid metabolism such as 3-hydroxy-3-methylglutaryl coenzyme A reductase, cholesteryl ester
transfer protein, lipoprotein lipase, and hepatic lipase and also the expression of LDL receptors.
Hence diabetes mellitus when associated with thyroid dysfunction leads to further
deterioration in glycemic control and lipid levels causing poor response to treatment.
Several studies have linked hyperlipidemia with cardiovascular morbidity. So thyroid
function may have a role in the treatment of hyperlipidemia and can prevent associated
cardiovascular morbidity13.
Yang GR et al demonstrated that diabetic patients with subclinical hypothyroidism are
found to have increased risk for developing retinopathy26. So it is important to evaluate diabetic
population regarding thyroid disorder whether clinical or subclinical, as one condition can
worsen the other if left untreated by causing worsening control of diabetes mellitus, worsening
dyslipidemias and causing diverse complications.
CONCLUSION:
Our findings indicate that thyroid dysfunction can produce significant metabolic
disturbance among patients with type 2 DM. Screening of thyroid dysfunction should be done in
all type 2 diabetic patients so that timely intervention can be done and patient’s health can be
improved.
ACKNOWLEDGEMENT: We acknowledge all the study subjects for being part of this study
and their cooperation. The authors are also grateful to authors / editors / publishers of all those
articles, journals and books from where the literature for this article has been reviewed and
discussed.
CONFLICT OF INTEREST: None.
FUNDS FOR THE STUDY: Nil.
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